Crystalline zeolite j



nited States atent Fatented Dec. 5, 1951' This invention relates to anovel composition of matter, and to a process for preparing andutilizing this novel material. More particularly, the invention isconcerned With a novel, synthetic member of the zeolite family.

The term zeolite, in general, refers to a group of naturally occurring,hydrated, metal aluminosllicates, many of which are crystalline instructure. The synthetic material of the invention has a compositionsimilar to certain of the natural crystalline zeolites. Accordingly, theterm synthetic zeolite is applied to the materials prepared by theprocess of the invention. There are, however, significant differencesbetween the synthetic and natural materials. For convenience anddistinguishability, the synthetic material of the invention will bereferred to hereinafter as zeolite I.

Crystalline zeolites structurally consist basically of an open,three-dimensional framework of SiO.; and MO; tetrahedra. The tetrahedraare cross-linked by the sharing of oxygen atoms, so that the ratio ofoxygen atoms to the total of the aluminum and silicon atoms is equal totwo, or O/(Al-i-Si) :2. The negative electrovalence of tetrahedracontaining aluminum is balanced by the inclusion Within the crystal ofcations, e.g., alkali metal or alkaline earth metal ions. This balancemay be expressed by the formula 2Al/ (ZNa, 2K, ZLi, Ca, Ba, Mg, Zn, Sr,etc.)=1. Moreover, it has been found that one cation may be replaced foranother by suitable exchange techniques. Consequently, crystallinezeolites are often employed as ion-exchange agents.-

It is also known that the crystal structures of many zeolites exhibitinterstices of molecular dimensions. The interstitial spaces aregenerally occupied by water of hydration. Under proper conditions, viz.,after at least partial dehydration, these zeolites may be utilized asefficient adsorbents whereby adsorbate molecules are retained within theinterstitial spaces. Access to these channels is had by way of orificesin the crystal lattice. 4

These openings limit the size and shape of the molecules that can beadsorbed. A separation of mixtures of foreign molecules based uponmolecular dimensions, wherein cer- .tain molecules are adsorbed by thezeolite while others are refused, is therefore possible. It is thischaracteristic property of many crystalline zeolites that has led totheir designation as molecular sieves. In addition to molecular size andshape, however, other factors may also influence the selectiveadsorption of certain foreign molecules by molecular sieves. Among thesefactors are: the polarizability and polarity of the adsorbate molecules;the degree of unsaturation of organic adsorbates; the size andpolarizing power of the interstitial cation; the presence of adsorbatemolecules in the interstitial spaces; and the degree of hydration of thezeolite.

A number of synthetic crystalline zeolites have been prepared. They aredistinguishable from each other, and from the naturally occurringmaterial, on the basis of their composition, crystal structure, andadsorption properties. A suitable method for distinguishing thesecompounds, for example, is by their X-ray powder difiraction patterns.The existence of a number of zeolites having similar but distinguishableproperties advantageously permits the selection of a particular memberhaving optimum properties for a particular use.

The present invention has as its prime object the previslon of a novel,synthetic, crystalline zeolite of the molecular sieve type. Anotherobject is to provide a novel, synthetic, crystalline zeolite havinguseful ion-exchange and adsorption properties. A further object is toprovide a convenient and efficient process for prepaing the novelmaterial of the invention.

The composition of crystalline zeolite I may stoichiometrically beexpressed, in terms of mole ratios oi oxides, as follows:

wherein x may be any value from 0 to about 1.4. Minor variations in themole ratios of these oxides, within the ranges indicated by the aboveformula, do not significantly change the crystal structure or physicalproperties of the zeolite.

In addition to composition, zeolite I may be identified, anddistinguished from other zeolites, and other crystalline substances, byits X-ray powder diffraction pattern, the data for which are set forthbelow in Table A. In obtaining the X-ray powder diffraction pattern,standard techniques were employed. The radiation was the K- alphadoublet of copper, and a Geiger counter spectrometer with a strip chartpen recorder was used. The peak heights, 1, and the positions as afunction of 20, where 6 is the Bragg angle, were read from thespectrometer chart. From these, the relative intensities, 1001/1 where Iis the intensity of the strongest line, or peak, and d(A.) observed, theinterplanar spacing in Angstrom units, corresponding to the recordedlines were determined.

Table A Relative l'nterplanar Bragg Angle 25 Intensity Spacing MA.)

100 I11 Observed 54 6. 86 11 5. 57 32 4. 77 16 4. 72 15 4. 27 51 4. 0O46 3. 23 4 3. 18 93 3. 13 4O 3. O4 41 3. 00 36 2. 97 100 2. 89 61 2. 8714 2. 68 20 2. 66 25 2. 64 11 2. 61 23 2. 58 14 2. 33 8 2. 30 14 2. 19 62. 15

The X-ray powder diffraction pattern for zeolite l indicates tetragonalunit cells having repeat distances of approximately 9.5 6 Angstrom unitsin two cell dimensions, and a repeat distance of approximately 9.92.Angstrom units in the third cell dimension.

The particular X-ray technique and/ or apparatus employed, the humidity,the temperature, the orientation of the powder crystals, and othervariables, all of which are well known and understood to those skilledin the art of X-ray crystallography or diffraction, may cause 3 somevariation in the intensities and positions of the X-ray lines. Thus, theX-ray data given herein to identify zeolite J are not to exclude thosematerials which, due to some variable mentioned above or otherwise knownto those skilled in the art, fail to show all of the tabulated X-raylines, or show a few extra ones permissible to the crystal system of thezeolite, or show a slight change in intensity or shift in position ofsome of the X-ray lines as set forth in Table A. p

In an embodiment of the present invention, zeolite I is prepared bysuitably heating an aqueous potassium aluminosilicate mixture whosecomposition, expressedin terms of mole ratios of om'des, falls withinthe following ranges:

K O/SiO of about 4 SiO A1 of about 4 H O/K O of about The desiredproduct is thereby crystallized out. In making zeolite J, representativereactants are silica gel, silicic acid, or potassium silicate as asource of silica. Alumina may be obtained from activated alumina, alphaalumina, gamma alumina, alumina trihydrate, aluminum hydroxide, hrpotassium aluminate. Potassium hydroxide may supply the potassium ions,and, in addition, assist in controlling the pH of the reactant mixture.Preferably, the reactants are water soluble. A solution of thereactants, in proper proportions, is placed in a container, made, forexample, of metal or glass. The container should be closed to preventloss of water. A convenient and preferred procedure for preparing thereactant mixture is to make an aqueous solution containing the potassiumaluminate and hydroxide, and add this, with agitation, to an aqueoussolution of potassium silicate. The resultant mixture is then stirred toinsure homogeneity.

For best results, the crystallization procedure is carried out at atemperature of approximately 100 C., the pressure being atmospheric, orat least that corresponding to the vapor pressure of Water inequilibrium with the mixture of reactants. Any suitable heatingapparatus, e.g., an

oven, sand bath, oil bath, or jacketed autoclave, may be used. Heatingis continued until the desired crystalline zeolite product is formed.The zeolite crystals are then filtered off and washed to separate themfrom the reactant mother liquor. The zeolite crystals should be washed,preferably with distilled water, until the effluent wash water, inequilibrium with the product, has a pH of between about 9 and 12. As thezeolite crystals are washed, some of the potassium ions in the zeolitemaybe removed, and are believed to be replaced by hydrogen ions. If thewashing is discontinued when the pH of the effluent wash water is about10, the K O/Al O molar ratio of the crystalline product will be betweenabout 0.9 and 1.0. Excessive washing will result in a somewhat lowervalue for this ratio, while insuflicient washing may leave slightexcesses of potassium associated with the product. Thereafter, thezeolite crystals may be dried, conveniently in a vented oven.

Typical of the manner in which zeolite I may be prepared is thefollowing example. A solution of potassium aluminate was prepared byinitially mixing 32.15 grams of potassium hydroxide, 3.0 grams ofaluminum hydroxwater, and heating the mixture until the reactantsdissolved. The solution was then cooled to room temperature, and addedto 23.73 grams of a potassium silicate solution containing 7.8 percentof K 0 and 19.3 percent of SiO by weight. The resulting mixture wasstirred until homogeneous. Crystallization of thedesired zeolite prod-.uct was carried out by heating the reactant mixture in a sealed glassjar at a temperature of 100 C. for approximately 89 hours. Thecrystalline product which formed had thereupon settled to the bottom ofthe jar, and the reactant mother liquid was clear. The crystallineproduct was then filtered, washed with water until the efiiuent wash\water had apH of about 10,5 to 11.0, and dried. Analy- .ide containing0.0192 mole of A1 0 and 31.54 ml. of

IA1203I 1.98102: 1.4H2O

X-rayanalysis of the product indicated a difiraction patterncharacteristic of zeolite J, as set forth above in Table A.

For satisfactory use as an adsorbent, zeolite I should be activated byat least partial dehydration. Such activation may be performed, forexample, by heating the zeolite to temperatures of approximately 350 C.under atmospheric or reduced pressure, or by maintaining the zeolite atroom temperature under vacuum. Unlike common adsorbents, such ascharcoal and silica gel, which show adsorption selectivities basedprimarily on the boiling point or critical temperature of the adsorbate,activated zeolite J exhibits a selectivity based on the size, degree ofunsaturation, and shape of the adsorbate molecule. Adsorption by zeoliteJ is generally limitedto small, polar molecules, such as Water, ammonia,and sulfur dioxide. Another property of zeolite I which contributes toits usefulness is that of adsorbing relatively large quantities ofadsorbate at either very low pressures or concentrations. The novelmaterial of this invention may therefore be utilized as a selectiveadsorbent in numerous gas or liquid separation processes, whereby small,polar molecules, particularly water, are separated from mixtures withother materials. The zeolite may also find use in cyclicadsorption-desorption processes for water, and possibly otheradsorbates.

Samples of zeolite I, prepared as described above, and which had beenactivated by dehydration at a temperature of approximately 350 C., undervacuum, were tested to determine their adsorption properties. Theresults obtained are set forth below in Table B. The adsorptionproperties were measured in a McBain adsorption system. The zeolitesamples were placed in light aluminum buckets suspended from quartzsprings. They were activated in situ, and the gas or vapor under testwas then admitted. The gain in weight of the adsorbent was measured bythe spring extensions asread by a cathetometer. In the Table B thepressure given for each adsorption is the pressure of the adsorbate. Theterm Weight percent adsorbed refers to the percentage increase in theweight of adsorbent.

Table B Tempera' Pressure Weight Adsorbate ture 0.) (mm. Hg) PercentAdsorbed From Table B, it can be seen, for example, that zeolite i,acting as a molecular sieve, will permit the separation of water from amixture with either carbon dioxide or ethylene.

Zeolite I may be used as an adsorbent for the purposes indicated abovein any suitable form. By way of illustration, a column of powderedcrystalline material may give excellent results, as may a pelleted formobtained by pressing into pellets a mixture of zeolite J and a suitablebonding agent such as clay.

Zeolite I may be ion-exchanged with other cations to form derivativesthereof by conventional ion-exchange techniques. A preferred, continuousmethod for ionexchange is to pack the zeolite into a series of verticalcolumns with suitable supports at the bottom; successively pass throughthe beds, at room temperature, a water solution of a soluble salt of thecation to be introduced into the zeolite; and change the flow from thefirst bed to the second as the zeolite in the first bed becomesionexchanged to the extent desired. Illustrative of convenientexchanging solutions are: for hydrogen exchange, a dilute water solutionof an acid such as hydrochloric acid; for sodium exchange, a watersolution of sodium chloride or dilute sodium hydroxide; for silverexchange, a Water solution of silver nitrate; for ammonium, calciumexchange, and the like, water solutions of the chlorides of thesecations. While it is more convenient to employ Water soluble compoundsof the cations to be exchanged, other solutions containing the desiredcations may also be employed. Moreover, particularly good results may beobtained by the utilization of an exchanging solution having a pH ofbetween about 5 and 12.

What is claimed is:

1. A synthetic, crystalline zeolite having a composition, expressed interms of mole ratios of oxides, as follows:

wherein x represents any value from 0 to about 1.4, said crystallinezeolite having an X-ray powder diffraction pattern essentially as shownin Table A.

2. The ion-exchanged forms of a synthetic, crystalline zeolite having acomposition, expressed in terms of mole ratios of oxides, as follows:

wherein x represents any value from O to about 1.4, said crystallinezeolite having an X-ray powder difiraction pattern essentially as shownin Table A, which process comprises preparing an aqueous potassiumaluminosilicate mixture whose composition, expressed in terms of moleratios of oxides, falls Within the following ranges:

K O/SiO of about 4 SiO /Al O Of about 4 H O/K O of about and maintainingsuch mixture at a temperature of approximately 100 C. until the desiredcrystalline zeolite product is formed.

4. A process for preparing a crystalline zeolite having a compositionexpressed in terms of mole ratios of oxides, as follows:

wherein x represents any value from 0 to about 1.4, said crystallinezeolite having an X-ray powder diffraction pattern essentially as shownin Table A, which process comprises preparing an aqueous potassiumaluminosilicate mixture whose composition, expressed in terms of moleratios of oxides, falls Within the following ranges:

K O/SiO of about 4 Of about 4 H O/K O of about 10 maintaining suchmixture at a temperature of approximately C. until the desiredcrystalline zeolite product is formed, and separating the resultantcrystals from the reactant mother liquor.

5. A process for preparing a crystalline zeolite having a compositionexpressed in terms of mole ratio of oxides as follows:

said crystalline zeolite having an X-ray powder diffraction patternessentially as shown in Table A, which process comprises preparing anaqueous potassium alumina-silicate mixture whose composition, expressedin terms of mole ratios of oxides, falls within the following ranges:

K O/SiO of about 4 SiO /Al O of about 4 H O/K O of about 10 andmaintaining such mixture at a temperature of approximately 100 C. untilthe desired crystalline zeolite product is formed.

6. A synthetic crystalline zeolite according to claim 1 wherein x isabout zero.

7. A process according to claim 4 wherein said crystalline zeoliteproduct is dehydrated at a temperature of approximately 350 C.

References Cited in the file of this patent UNITED STATES PATENTS1,949,360 Schorger Feb. 27, 1934 1,965,923 Griesbach et a1. July 10,1934 2,467,215 McCarter Apr. 12, 1949 2,560,931 Chapman et a1. July 17,1951 2,790,512 Dow Apr. 30, 1957 2,810,455 Veltman Oct. 22, 19572,882,244 Milton Apr. 14, 1959 OTHER REFERENCES Barrer et al.: J. Chem.800., Part 3, pp. 2882-2903 (1956).

0.9$0.1K2O:2.1$0.2SIO2:XH2O
 3. A PROCESS FOR PREPARING A CRYSTALLINEZEOLITE HAVING A COMPOSITION EXPRESSED IN TERMS OF MOLE RATIOS OFOXIDES, AS FOLLOWS: